This invention relates to an endoscope in which an objective unit is replaceable.
As one example of such an endoscope, an electronic endoscope will be described. The endoscope includes a body having a hollow base portion, and a hollow insert portion extending through the base portion. An objective optical system is received in a distal end portion of the insert portion. An image sensor (light receiving means) such as a CCD or the like is disposed backwardly of the objective optical system. Signal lines (image transmission means) are connected to the image sensor. The signal lines extend through both the insert portion and the base portion and is introduced outside. A distal end portion of an optical fibers bundle (illumination light transmission means) is received in the distal end portion of the insert portion. This optical fibers bundle extends through both the insert portion and the body and is introduced outside. A rear end of the optical fibers bundle is connected to a light source device. Illumination light from the light source device passes through the optical fibers bundle and is irradiated from a distal end face of the optical fibers bundle at the distal end portion of the insert portion. An image of an observation object is taken by the image sensor through the objective optical system and an image signal thereof is transmitted to a processor through the signal lines. Then the image signal is converted to a television signal and displayed on a television set.
The endoscope of the type mentioned above is sometimes required to provide a wide angle view and a telescopic view. Also, the endoscope is required to provide different view fields such as a forward sight, a sideward sight, etc.
To meet with such requirements, if a plurality of endoscopes having different tasks are to be employed, the costs will be increased. In view of the foregoing, endoscopes are developed as disclosed in Japanese Patent Application Laid-Open No. 196718/1985 and Japanese Utility Model Application Laid-Open No. 69116/1991, in which an objective unit constituted of a sleeve-like support and an objective optical system received in the support is detachably attached to a distal end portion of an insert portion. In such endoscopes, interference between the objective optical system and illumination light transmission means is a problem to be solved. For example, as shown in FIG. 1 of Japanese Utility Model Application Laid-Open No. 69116/1991, illumination light from the illumination light transmission means is partly shaded by a support of an objective unit and as a consequence, the illumination light cannot be supplied over a wide range of area. On the contrary, if an arrangement is made such that a distal end of the optical fibers bundle projects forwardly of the objective optical system, the observation view field is shaded by the illumination light transmission means.
Accordingly, as disclosed in FIG. 2 of Japanese Utility Model Application Laid-Open No. 69116/1991 and Japanese Patent Application Laid-Open No. 196718/1985, the objective unit comprises not only an objective optical system but also a short optical fibers bundle used for illumination light transmission. The objective optical system and the optical fibers bundle are such arranged to have a positional relation that no interference occurs therebetween.
However, in the above-mentioned embodiment, since the objective unit has the objective lens and the optical fibers bundle incorporated therein, the construction becomes complicated and the manufacturing costs are increased. Further, the illumination light transmission means is split into a long optical fibers bundle on the insert portion side and the short optical fibers bundle on the objective unit side, and transmission losses of the illumination light occur at joint interfaces of both of them. In order to compensate the transmission losses, it is required that the optical fibers bundle is increased in sectional area. As a consequence, an outer diameter of the insert portion is increased. Furthermore, leak of light occurs at the joint interfaces and observation is interfered by that.